Shelf



FIG. 1 is a front/right/top perspective view of a shelf (a front/left/top perspective view would be a mirror image thereof);

FIG. 2 is a rear/right/bottom perspective view thereof (a rear/left/bottom perspective view would be a mirror image thereof);

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevational view thereof (a rear elevational view would be a mirror image thereof); and,

FIG. 6 is a right side elevational view thereof (a left side elevational view would be a mirror image thereof).

The broken lines depict portions of the shelf that form no part of the claimed design. 

CLAIM I claim the ornamental design for a shelf, as shown and described. 